Method of making halophthalic acids and halophthalic anhydrides

ABSTRACT

A method of preparing a halophthalic acid is disclosed which comprises the steps of contacting in a liquid phase reaction mixture at least one halogen-substituted ortho-xylene with oxygen and acetic acid at a temperature in a range between about 120° C. and about 220° C. in the presence of a catalyst system yielding a product mixture comprising less than 10 percent halogen-substituted ortho-xylene starting material, a halophthalic acid product, and less than about 10,000 ppm halobenzoic acid and less than about 1000 ppm halophthalide by-products based on a total amount of halophthalic acid present in the product mixture. In addition methods for the preparation of halophthalic anhydride, and recovery of high purity acetic acid from an aqueous acetic acid stream comprising HCl, which is generated during the preparation of the halophthalic acid are also disclosed.

This application is a Continuation in Part of U.S. patent applicationSer. No. 10/882,762, entitled “METHOD OF MAKING HALOPHTHALIC ACIDS ANDHALOPHTHALIC ANHYDRIDES” filed on Jun. 30, 2004 now abandoned, which isherein incorporated by reference.

BACKGROUND OF THE INVENTION

This invention relates to a method of preparing substituted aromaticcarboxylic acid compounds. In particular, the present invention relatesto liquid phase reaction of halogen-substituted ortho-xylene to producehalophthalic acid and halophthalic anhydride.

Oxidation of dialkyl benzenes has long been used to produce dicarboxylicacids. The oxidation has also been carried out in liquid phase inpresence of a solvent. Of particular interest has been the oxidation ofdimethyl benzene (xylene) to phthalic acid and the oxidation ofpara-xylene to terephthalic acid, which is in turn employed in theproduction of polybutylene terephthalate. Various methods for oxidizingortho-xylene are known. For example, U.S. Pat. No. 3,402,184 describesoxidation of ortho-xylene in acetic acid solvent in the presence of abromine promoter. U.S. Pat. Nos. 5,958,821; 5,981,420; and 6,020,522describe oxidation of ortho-xylene in acetic acid solvent in thepresence of a hydroxyimide promoter. Methods for preparing4-chlorophthalic anhydride are also known. However, these methodstypically involve aromatization of a Diels-Alder adduct of chloropreneand a maleic anhydride as in U.S. Pat. No. 5,322,954, or chlorination ofphthalic acid as in Japanese patent applications 07258152 and 02129143.The chlorination process may also produce highly undesirablepolychlorinated biphenyls. There is a need for a method for producing4-chlorophthalic anhydride which does not involve handling toxicchloroprene or chlorine gas.

The liquid phase oxidation of xylene to phthalic acid requires the useof a catalyst, typically a cobalt/manganese/bromide catalyst system, andis generally performed in a carboxylic acid solvent such as acetic acid.The catalyst system may be augmented by the use of a co-catalyst such aszirconium, hafnium or cerium. Phthalic acid is an easily isolable solid,which can be filtered out of the reaction mixture.

Liquid phase oxidation, using a cobalt/manganese/bromide catalyst systemand a carboxylic acid solvent, has also been applied to halogenatedxylene with some success. The oxidation of the halogenated xylene is,however, more difficult than the oxidation of xylene due to presence ofa halogen, which is an electron withdrawing substituent, on the benzenering. The greater difficulty in oxidation results in a lower reactionselectivity and a larger amount of partial oxidation and side productsthan seen in the liquid phase oxidation of xylene under similarconditions. Additionally, the relatively soluble halogenated phthalicacid is difficult to separate from the partial oxidation and sideproducts. Thus it is clear that in order for a method of halogenatedxylene liquid phase oxidation to be successful, the reaction yield andthe reaction selectivity must be very high and by-product formationshould be minimized. Furthermore, in order to improve the commercialattractiveness of the liquid phase oxidation of halogenated xylene,effective methods for recovering high purity acetic acid (ex., up to99.9 weight percent purity and having less than 0.01 weight percent ofHCl) for reuse in the oxidation reaction are also desirable.

BRIEF SUMMARY OF THE INVENTION

In one aspect, the present invention provides a method of preparing ahalophthalic acid I

wherein X is a fluorine, chlorine, bromine, or iodine atom; said methodcomprising the steps of contacting in a liquid phase reaction mixture atleast one halogen-substituted ortho-xylene with oxygen and acetic acidat a temperature in a range between about 120° C. and about 220° C. inthe presence of a catalyst system. The catalyst system consistsessentially of a source of cobalt ions, a source of manganese ions, anda source of bromide ions. The reaction mixture is characterized by aninitial molar ratio of cobalt ion to halogen-substituted ortho-xylene ofless than about 2%, an initial molar ratio of manganese ion tohalogen-substituted ortho-xylene of less than about 1.5%, and an initialmolar ratio of bromide ion to halogen-substituted ortho-xylene of lessthan about 0.5%. The oxygen is present in an amount corresponding to apartial pressure of oxygen in a range between about 0.00001 and about 15bar. The product mixture comprises less than 10 percenthalogen-substituted ortho-xylene starting material and a halophthalicacid product. In addition, the product mixture contains less than about10,000 parts per million (ppm) halobenzoic acid by-product and less thanabout 1000 parts per million (ppm) halophthalide by-product based on atotal amount of halophthalic acid present in the product mixture.

In another aspect, the present invention relates to a method ofpreparing a halophthalic anhydride comprising less than about less thanabout 500 parts per million halobenzoic acid by-product and less thanabout 500 parts per million halophthalide by-product.

In yet another aspect, the present invention provides a method ofpreparing a halophthalic acid wherein the acetic acid employed duringone or more steps of the process is recovered for reuse. The methodcomprises the steps of: Step (A) contacting in a liquid phase reactionmixture at least one halogen-substituted ortho-xylene with oxygen andacetic acid at a temperature in a range between about 120° C. and about220° C. in the presence of a catalyst system to provide a first productmixture comprising less than 10 percent halogen-substituted ortho-xylenestarting material, a halophthalic acid product, and less than about10,000 parts per million halobenzoic acid by-product, and less thanabout 1000 parts per million halophthalide based on a total amount ofhalophthalic acid present in the first product mixture; and Step (B)stripping a mixture comprising water, acetic acid, and hydrochloric acidfrom the first product mixture; to afford the crude halophthalic acidand a crude recovered acetic acid solvent comprising water, acetic acid,and hydrochloric acid.

The catalyst system employed in Step (A) consists essentially of asource of cobalt, ion, a source of manganese ions, and a source ofbromide ions. The reaction mixture of Step (A) is characterized by aninitial molar ratio of cobalt ion to halogen-substituted ortho-xylene ofless than about 2%, an initial molar ratio of manganese ion tohalogen-substituted ortho-xylene of less than about 1.5%, and an initialmolar ratio of bromide ion to halogen-substituted ortho-xylene of lessthan about 0.5%. The oxygen is present in the reaction mixture in anamount corresponding to a partial pressure of oxygen in a range betweenabout 0.0001 and about 15 bar.

In a further aspect of the invention, distillation techniques areprovided for recovering purified acetic acid from the crude recoveredacetic acid solvent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the Influence of post-oxidation duration on by-productformation during oxidation of chloro-o-xylene under standard conditions.

FIG. 2 shows the influence of bromide level on formation of by-productsduring oxidation of chloro-o-xylene under standard conditions.

FIG. 3 shows the influence of catalyst level on formation of by-productsduring oxidation of chloro-o-xylene.

DETAILED DESCRIPTION OF THE INVENTION

The present invention may be understood more readily by reference to thefollowing detailed description of preferred embodiments of the inventionand the examples included herein. In this specification and in theclaims which follow, reference will be made to a number of terms whichshall be defined to have the following meanings.

The singular forms “a”, “an” and “the” include plural referents unlessthe context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where the event occurs and instances where it does not.

“Ortho-xylene” used herein is also known as 1,2-dimethylbenzene.

As used herein the term “aromatic radical” refers to a radical having avalence of at least one and comprising at least one aromatic ring.Examples of aromatic radicals include phenyl, pyridyl, furanyl, thienyl,naphthyl, phenylene, and biphenyl. The term includes groups containingboth aromatic and aliphatic components, for example a benzyl group, aphenethyl group or a naphthylmethyl group. The term also includes groupscomprising both aromatic and cycloaliphatic groups for example4-cyclopropylphenyl and 1,2,3,4-tetrahydronaphthalen-1-yl.

As used herein the term “aliphatic radical” refers to a radical having avalence of at least one and consisting of a linear or branched array ofatoms which is not cyclic. The array may include heteroatoms such asnitrogen, sulfur and oxygen or may be composed exclusively of carbon andhydrogen. Examples of aliphatic radicals include methyl, methylene,ethyl, ethylene, hexyl, hexamethylene and the like.

As used herein the term “cycloaliphatic radical” refers to a radicalhaving a valance of at least one and comprising an array of atoms whichis cyclic but which is not aromatic, and which does not further comprisean aromatic ring. The array may include heteroatoms such as nitrogen,sulfur and oxygen or may be composed exclusively of carbon and hydrogen.Examples of cycloaliphatic radicals include cyclopropyl, cyclopentylcyclohexyl, 2-cyclohexylethy-1-yl, tetrahydrofuranyl and the like.

As, noted, the present invention relates to a method of preparingsubstituted aromatic carboxylic acid compounds. In particular, thepresent invention relates to liquid phase reaction ofhalogen-substituted ortho-xylene to produce a halophthalic acid whichmay be converted to a halophthalic anhydride.

In one embodiment said at least one halogen-substituted ortho-xylene isa monohalo-ortho-xylene. The halogen substituent may be in the 3position (the 3-isomer) or in the 4 position (the 4-isomer). Thehalogen-substituted ortho-xylene used may also be a mixture of the3-isomer and the 4-isomer. The halogen may be selected from fluorine,chlorine, bromine, or iodine. In one particular embodiment thehalogen-substituted ortho-xylene is a 4-halo ortho-xylene, for example4-fluoro- or 4-chloro-ortho-xylene. In another embodiment thehalogen-substituted ortho-xylene is a mixture comprising 4-halo- and3-halo-ortho-xylenes, for example a mixture of 4-fluoro- and3-fluoro-ortho- xylene. In another particular embodiment thehalogen-substituted ortho-xylene is a mixture of 4-chloro-ortho-xylene(also known as 4-chloro-1,2-dimethylbenzene) and 3-chloro-ortho-xylene(also known as 3-chloro-1,2-dimethylbenzene). In one embodiment themixture of 4-chloro-1,2-dimethylbenzene and 3-chloro-1,2-dimethylbenzenecomprises at least about 95 mole percent of3-chloro-1,2-dimethylbenzene. In another embodiment the mixture of4-chloro-1,2-dimethylbenzene and 3-chloro-1,2-dimethylbenzene comprisesat least about 95 mole percent of 4-chloro-1,2-dimethylbenzene. In yetanother embodiment the halogen-substituted ortho-xylene consistsessentially of 4-chloro-1,2-dimethylbenzene. When 3-halo-ortho-xylene ispresent, it comprises in some embodiments about 0.001-35 molar percent,in other embodiments about 0.001-15 molar percent, in other embodimentsabout 0.01-12 molar percent, and in still other embodiments about 0.1-10molar percent of total halogen-substituted ortho-xylene substrateundergoing oxidation.

According to the method of the present invention a halogen-substitutedortho-xylene is converted to a halogen-substituted phthalic acid bycontacting in a liquid phase the halogen-substituted ortho-xylene in thepresence of at least one solvent, which in some embodiments comprises alower aliphatic carboxylic acid. Illustrative examples of loweraliphatic carboxylic acids employed in the present invention, include,but are not limited to, acetic acid, propionic acid, butanoic acid,pentanoic acid, or hexanoic acid. In one embodiment the lower aliphaticcarboxylic acid is acetic acid. In some instances anhydrous acetic acidmay be employed. Alternatively a mixture of acetic acid and water may beemployed. In one embodiment the acetic acid may contain up to about 3percent by weight water. Typically the acetic acid is present in anamount of about 7 to about 3 parts by weight to 1 part by weight ofhalo-substituted ortho-xylene. Preferably the acetic acid is present inan amount of about 5 to about 3 parts by weight to 1 part by weight ofhalogen-substituted ortho-xylene. The solvent may be recovered andreused following the reaction. For example, in some embodiments theproduct mixture is stripped to dryness to remove essentially allvolatile materials, including, but not limited to, solvent beforefurther treatment.

The catalyst system consists essentially of a source of cobalt ion, asource of manganese ion and a source of bromide ion. Useful cobalt,manganese, and bromine sources are those sources, which provide solubleforms of ionic cobalt, ionic manganese, and ionic bromine. Cobalt, andmanganese sources that may be used include the metals themselves or anyof their salts, complexes or compounds, and organometallic compounds.These cobalt, and manganese sources include, but are not limited to,cobalt and manganese acetates, citrates, stearates, napthenates,acetylacetonates, benzoylacetonates, carbonates, sulfates, bromides,chlorides, fluorides, nitrates, hydroxides, alkoxides, nitrides,triflates, hydrates of the foregoing, and mixtures of the foregoing.

In one embodiment of the present invention the source of cobalt ions isat least one cobalt containing species selected from the groupconsisting of metallic cobalt, salts of cobalt, complexes andorganometallic compounds containing cobalt. In one embodiment the cobaltin the cobalt source is in a +2 or +3 oxidation state. In one embodimentthe source of cobalt ions is at least one species selected from thegroup consisting of cobalt sulfate, cobalt bromide, cobalt chloride,cobalt fluoride, cobalt iodide, cobalt nitrate, cobalt stearate, cobaltcarbonate, cobalt naphthalate, cobalt (II) hydroxide, cobalt (II)phosphate, cobalt (III) fluoride, cobaltous acetate, cobalt(II)acetylacetonate, cobalt (II) benzoylacetonate, cobalt(III)acetylacetonate, and cobalt(II) hexafluoroacetylacetonate, andcombinations thereof.

In some embodiments the source of manganese ions is at least onemanganese containing species selected from the group consisting ofmetallic manganese, salts of manganese, complexes and organometalliccompounds containing manganese. In one embodiment of the presentinvention the source of manganese ions is a manganese compound in a +2or +3 oxidation state. Suitable sources of manganese ions includemanganese (II) fluoride, manganese (II) chloride, manganese (II)bromide, manganese (II) iodide, manganese (III) fluoride, manganese (II)acetate, manganese sulfate, manganese nitrate, manganese carbonate,manganese (III) acetate, manganese(II) acetylacetonate, manganese(III)acetylacetonate, manganese (II) hexafluoroacetylacetonate, and manganese(III) hexafluoroacetylacetonate, and combinations thereof.

The source of bromide ions is at least one bromine-containing speciesselected from the group consisting of inorganic bromide salts, organicbromide salts, inorganic bromine compounds comprising covalently boundbromine (e.g. BrCl), organic bromine compounds comprising covalentlybound bromine, and elemental bromine. Suitable sources of bromide ioninclude alkali metal bromides, alkaline earth metal bromides, lanthanidemetal bromides, transition metal bromides, quaternary ammonium bromides,quaternary phosphonium bromides, tetrabromosilane, acetyl bromide,oxalyl bromide, carbonyl dibromide, and tertiary-butyl bromide.Additional examples of inorganic bromide ion sources include bromine andhydrogen bromide. Additional examples of organic organic bromide ionsources include tetrabromoethane, ethyl bromide, ethylene bromide,bromoform, xylyl bromide, xylylene bromide and mixtures thereof may beemployed as a source of bromide ions.

The amounts of the various catalyst system components are convenientlyexpressed in terms of mole percent (mol %) of the cobalt, manganese, andbromine ions present and are based on the amount of halogen-substitutedortho-xylene present at the beginning of the reaction. Typically thecobalt source is generally present in amount corresponding to about 0.25to about 2 mole percent cobalt ion relative to the halogen-substitutedortho-xylene at the outset of the reaction. In another embodiment thecobalt source is present in amount corresponding to about 0.5 to about1.5 mole percent cobalt ion relative to the halogen-substitutedortho-xylene at the outset of the reaction. In yet another embodimentthe cobalt source is present in amount corresponding to about 1 to about1.5 mole percent cobalt ion relative to the halogen-substitutedortho-xylene at the outset of the reaction.

The manganese source is present in an amount corresponding to about 0.25mole percent to about 1.5 mole percent manganese ion relative to theamount of halogen-substituted ortho-xylene at the outset of thereaction. In one embodiment the manganese source is present in an amountcorresponding to about 0.5 mole percent to about 1.25 mole percentmanganese ion relative to the amount of halogen-substituted ortho-xyleneat the outset of the reaction. In another embodiment the manganesesource is present in an amount corresponding to about 0.6 mole percentto about 1.0 mole percent manganese ion relative to the amount ofhalogen-substituted ortho-xylene at the outset of the reaction.

The bromide source is present in an amount corresponding to about 0.005mole percent to about 0.5 mole percent relative to the amount ofhalogen-substituted ortho-xylene at the outset of the reaction. In oneembodiment of the present invention the amount of the bromine source ispresent in an amount corresponding to about 0.05 mole percent to about0.5 mole percent relative to the amount of halogen-substitutedortho-xylene at the outset of the reaction. In yet another embodiment,the bromide source is present in an amount corresponding to about 0.15mole percent to about 0.35 mole percent relative to the amount ofhalogen-substituted ortho-xylene at the outset of the reaction. It hasbeen discovered that in liquid phase oxidations employinghalogen-substituted ortho-xylene the amount of bromide can have asignificant impact on the amount of impurities present in the finalproduct. It has been discovered that the use of decreasing molarpercentages of bromide results in a product, either halophthalic acid oranhydride, with a decreased level of impurities such as halophthalideand halobenzoic acids. Lower levels of bromide, such as molarpercentages less than about 0.35, may be useful in producing high purityhalophthalic acid or anhydride in even very large scale liquid phaseoxidations such as those employing thousands of kilograms ofhalogen-substituted ortho-xylene.

Suitable molecular oxygen containing gases include gases or combinationsof gases which are a source of molecular oxygen (O₂), for example, 100percent oxygen and mixtures of oxygen with one or more inert gaseswherein the concentration of oxygen is sufficient to effect oxidationunder the reaction conditions. The oxygen source used in the presentinvention may be high purity oxygen molecular oxygen, air,oxygen-enriched air, or oxygen diluted with another gas which has nonegative effects on the reaction, such as nitrogen, and noble gases suchas helium and argon. In one embodiment of the present invention thediluent gas is nitrogen. The concentration of diluent gas, when present,in the oxygen source is typically in a range between about 1 to about 95volume percent, preferably about 10 to about 80 volume percent. In oneembodiment the oxygen source is oxygen-enriched air containing about 28mole percent oxygen. As will be appreciated by one of skill in the art,the concentration of oxygen may affect the rate of the reaction.

Oxygen in the form of an oxygen source may be introduced into thereaction mixture by any convenient means. In one embodiment the reactionmixture is agitated or stirred under a positive pressure of the oxygensource, for example a positive pressure of an oxygen-nitrogen gasmixture. In one embodiment of the present invention oxygen is presentduring the oxidation reaction in an amount corresponding to a partialpressure of oxygen in a range between about 0.00001 and about 15 bar.Alternatively the oxygen is present in an amount corresponding to apartial pressure of oxygen in a range between about 0.001 and about 10bar. In yet another embodiment the oxygen is present in an amountcorresponding to a partial pressure of oxygen in a range between about0.01 and about 1 bar.

In an exemplary process, the halophthalic acid may be produced bycontacting the halogen-substituted ortho-xylene with oxygen, the cobaltsource, the manganese source and the bromide source in a solution inacetic acid in a pressurized reaction vessel. The contacting is carriedout at a temperature effective to promote oxidation of at least one andpreferably both methyl groups of the halogen-substituted ortho-xylene inthe presence of the catalyst and oxygen source. Preferably the reactionmixture is heated to a temperature in a range between about 80° C. andeither the temperature at which either catalyst or promoter is no longereffective for promoting reaction or the effective boiling point of thereaction mixture under the prevailing pressure, whichever of the two isthe lower temperature. The temperature of the reaction is typicallyabout 120° C. to about 220° C. More preferably the reaction mixture isheated to a temperature in a range of between about 150° C. and about190° C. The contacting is carried out at a pressure of in a rangebetween about 10 and about 30 bar, preferably in a range between about18 and about 25 bar.

Typically the molecular oxygen containing gas is introduced throughoutthe course of the oxidation reaction. In one embodiment the molecularoxygen containing gas is introduced to the reaction mixture and the flowof the molecular oxygen containing gas is maintained at a rate thatcreates an oxygen containing off gas with an oxygen concentration ofless than about 6 percent by volume, preferably less than about 4percent by volume. The off gas oxygen concentration may be determined byparamagnetic oxygen transduction analysis or other method known in theart. Useful flow rates are typically greater than or equal to 0.5 normalcubic meter (m³)/hour per kilogram (kg) of halogen-substitutedortho-xylene and preferably greater than or equal to 1.0 normal cubicmeter (m³)/hour per kilogram (kg) of halogen-substituted ortho-xylene. Anormal cubic meter is defined as cubic meter under standard temperatureand pressure condition. Preferably the reaction mixture is agitatedusing standard methods such as mechanical stirring. The flow of themolecular oxygen containing gas continues until the off gas oxygenconcentration exceeds about 4 percent by volume, indicating a slowing ofthe reaction. Once the off gas oxygen concentration exceeds about 4percent by volume the flow of the molecular oxygen containing gas ismodified so as to maintain the off gas oxygen concentration below about5 percent by volume and the temperature of the reaction may beincreased. It is preferable, however, for the temperature to remainbelow about 200° C. The flow of the molecular oxygen containing gas maybe modified in several ways. The molecular oxygen containing gas may bediluted with an inert gas so as to decrease the oxygen concentration inthe molecular oxygen containing gas, the flow rate of the molecularoxygen containing gas may be decreased, the source of the molecularoxygen containing gas may be changed so as to employ a molecular oxygencontaining gas with a lower oxygen concentration or these methods may becombined so as to maintain the off gas oxygen concentration below about5 percent by volume. The modified flow of molecular oxygen containinggas is continued until at least about 90 percent of halogen-substitutedortho-xylene has been converted to halophthalic acid, preferably untilgreater than 95 percent has been converted. The amount of conversionachieved in the reaction can readily be determined through the use ofgas chromatography, mass spectrometry, or other methods known in the artsuch as high performance liquid chromatography (HPLC).

After the reaction reaches the desired level of conversion, thehalophthalic acid may be recovered as a product mixture comprisinghalophthalic acid I and halophthalic anhydride II

wherein X is a fluorine, chlorine, bromine, or iodine atom. Halophthalicacid and halophthalic anhydride with a high degree of purity arerequired for various applications. Such high degree of purity may beachieved by the method described herein. By-products produced includethe isomeric halobenzoic acids III, and the isomeric halophthalides IV

wherein X is a fluorine, chlorine, bromine, or iodine atom. It should benoted that there are 3 possible isomeric forms of halobenzoic acids III:(i) X in the “2” position, (ii) X in the “3” position, and (iii) X inthe “4” position. There are 4 such isomers possible for halophthalidesIV: (i) X in the “4” position, (ii) X in the “5” position, (iii) X inthe “6” position, and (iv) X in the “7” position. In one embodiment ofthe present invention, halophthalic acid and halophthalic anhydrideproducts prepared by the method of the present invention contain lessthan about 1000 parts per million of halophthalide (all halophthalideisomers), preferably less than about 600 parts per million ofhalophthalide, and more preferably less than about 500 parts per millionof halophthalide. Additionally, halophthalic acid and halophthalicanhydride containing less than about 1 percent by weight of phthalicanhydride (the product of dehalogenation) may also be achieved. Inanother embodiment of the present invention the product mixturecomprises less than about 10,000 parts per million of halobenzoic acidbased on a total amount of halophthalic acid present in the initiallyformed product mixture. In yet another embodiment the initially formedproduct mixture comprises less than about 8,000 parts per million ofhalobenzoic acid. In a preferred embodiment of the present invention theinitially formed product mixture comprises less than about 5,000 partsper million of halobenzoic acid.

In one embodiment of the present invention the method of preparing ahalophthalic acid comprises oxidation products resulting from oxidationof at least one of and sometimes both the two ortho-methyl groups of thehalogen-substituted ortho-xylene. In various embodiments the oxidationproducts comprise at least one of a substituted or unsubstitutedortho-benzene dicarboxylic acid (also known as phthalic acid), or asubstituted or unsubstituted aromatic anhydride derived from thecorresponding ortho-benzenedicarboxylic acid (also known as phthalicanhydride). In one embodiment the oxidation products comprise at leastone of phthalic acid, phthalic anhydride, halotoluic acid, halophthalicacid, halophthalic anhydride, or mixtures thereof. In still anotherembodiment the oxidation products comprise at least one of phthalicacid, phthalic anhydride, chlorotoluic acid, 3-chlorophthalic acid,3-chlorophthalic anhydride, 4-chlorophthalic acid, 4-chlorophthalicanhydride, or mixtures thereof. It is understood that product mixturesinitially comprising halophthalic acid may be dehydrated to form aproduct mixture comprising in some embodiments up to 100 mole percent(based on halophthalic acid) of halophthalic anhydride. It is alsounderstood that product mixtures initially comprising halophthalicanhydride may be hydrated to form a product mixture comprising in someembodiments up to 100 mole percent (based on halophthalic anhydride) ofhalophthalic acid. In a particular embodiment the initially formedoxidation product comprises chlorotoluic acid, 4-chlorophthalic acid,and 4-chlorophthalic anhydride. In another particular embodiment theinitially formed oxidation product comprises isomeric chlorotoluic acidsand a mixture of 3-chloro- and 4-chlorophthalic acid, and 3-chloro- and4-chlorophthalic anhydride. When ortho-xylene is present as acontaminant in the halogen-substituted ortho-xylene undergoingoxidation, then phthalic acid phthalic anhydride, and/or toluic acid maybe present in the initially formed oxidation product.

In one aspect the present invention provides a method of preparing ahalophthalic anhydride. A first reaction mixture is formed by contactingin a liquid phase reaction mixture at least one halogen-substitutedortho-xylene with oxygen and acetic acid at a temperature in a rangebetween about 120° C. and about 220° C. in the presence of a catalystsystem, consisting essentially of a source of cobalt, ion, a source ofmanganese ions, and a source of bromide ions, said reaction mixturebeing characterized by an initial molar ratio of cobalt ion tohalogen-substituted ortho-xylene of less than about 2%, an initial molarratio of manganese ion to halogen-substituted ortho-xylene of less thanabout 1.5%, and an initial molar ratio of bromide ion tohalogen-substituted ortho-xylene of less than about 0.5%, said oxygenbeing present in an amount corresponding to a partial pressure of oxygenin a range between about 0.0001 and about 15 bar. Following theoxidation reaction, a first product mixture is obtained which comprisesless than about 10 percent of the total amount of halogen-substitutedortho-xylene starting material (i.e., conversion>90%) less than about10,000 parts per million halobenzoic acid and less than about 1000 partsper million halophthalide based on a total amount of halophthalic acidpresent in the product mixture. In another embodiment the first productmixture comprises less than about 5 percent halogen-substitutedortho-xylene starting material and less than about 10,000 parts permillion halobenzoic acid and less than about 1000 parts per millionhalophthalide based on a total amount of halophthalic acid present inthe product mixture. In yet another embodiment the first product mixturecomprises less than about 10 percent halogen-substituted ortho-xylenestarting material and less than about 5,000 parts per millionhalobenzoic acid and less than about 500 parts per million halophthalidebased on a total amount of halophthalic acid present in the productmixture. In a preferred embodiment of the present invention the firstproduct mixture comprises less than about 5 percent halogen-substitutedortho-xylene starting material and less than about 5,000 parts permillion halobenzoic acid and less than about 500 parts per millionhalophthalide based on a total amount of halophthalic acid present inthe product mixture. In an alternate preferred embodiment of the presentinvention the first product mixture comprises less than about 2 percenthalogen-substituted ortho-xylene starting material and less than about5000 parts per million of halobenzoic acid and less than about 500 partsper million halophthalide based on a total amount of halophthalic acidpresent in the product mixture.

The conversion of the product halophthalic acid to halophthalicanhydride can effected by stripping water and acetic acid from the firstproduct mixture and effecting ring closure of the halophthalic acid. Thestripping of water and acetic acid from the first product mixture iscarried out at ambient pressure temperature in the range of betweenabout 100° C. and about 120° C. Alternatively, the stripping of waterand acetic acid can be carried out at sub-atmospheric pressure. In oneembodiment a stripping regime includes stripping at both atmospheric andsub-atmospheric pressure.

The first product mixture typically comprises the product halophthalicacid, by-product halobenzoic acids, by-product halophthides, andresidual catalyst mixture. In one embodiment of the present inventionthe first product mixture is subjected to conditions which effect ringclosure of the product halophthalic acid to afford a second productmixture comprising halophthalic anhydride, the halobenzoic acids, thehalophthalides and the residual catalyst mixture.

In one embodiment of the present invention a first “evaporativeseparation” is performed on the second product mixture in order toseparate the product halophthalic anhydride from residual catalystmixture. The term “evaporative separation” includes such techniques asdistillation, thin film evaporation, sublimation and vacuum transfer,and generally refers to a process in which volatile components of aproduct mixture are separated from non-volatile components in theproduct mixture. Typically, vacuum distillation or thin film evaporationis preferred. This first evaporative separation typically affords adistillate ( the “third product mixture”) comprising a purifiedhalophthalic anhydride and a residual catalyst mixture comprisinghalophthalic anhydride, halobenzoic acids, halophthalides, andcomponents of the catalyst system employed. In yet another embodiment asecond “evaporative separation” of the purified halophthalic anhydride(the third product mixture) is carried out to afford a halophthalicanhydride comprising less than about 1000 parts per million of ahalobenzoic acid and less than about 500 parts per millionhalophthalide. In a preferred embodiment of the present invention thehalophthalic anhydride obtained from the second evaporative separationcomprises less than about 500 parts per million of halobenzoic acid andless than about 100 parts per million halophthalide.

The residual catalyst mixture may be recovered and reused in oxidationreactions of the type disclosed by the present invention. Such recyclingof the catalyst system affords a variety of economic and environmentalbenefits. In one embodiment of the present invention the residualcatalyst mixture is used as an additional source of cobalt ions,manganese ions, and bromide ions for the oxidation of a halo-substitutedortho-xylene starting material.

Most of the acetic acid as well as water produced in the oxidationreaction can be removed by distillation. The acetic acid and water areremoved as a vapor and condensed. The water may then be removed from theacetic acid and the acetic acid may be recycled. Some dehydration of thehalophthalic acid to form halophthalic anhydride may occursimultaneously with the removal of acetic acid and water. Furthermore,the removal of acetic acid and water may be combined with dehydration ofthe halophthalic acid in a single step. Dehydration is typically carriedout thermally by distillation under vacuum at an elevated temperature.Dehydration may also be carried out by other chemical reactions wellknown to those skilled in the art such as treatment with aceticanhydride. After distillation, the purity of the halophthalic anhydrideis typically greater than about 95 percent, preferably greater thanabout 97 percent, and most preferably greater than about 99 percent asmeasured by gas chromatography.

In one aspect the present invention provides a method for thepreparation of a polyetherimide comprising structural units derived fromthe halophthalic anhydride provided by the present invention. Methodsfor the preparation polyetherimides comprising structural units derivedfrom a halophthalic anhydride are known in the art, for example, U.S.Pat. Nos. 5,917,005 and 6,020,456 which are incorporated herein byreference in their entirety. Thus in one aspect, the halophthalicanhydride comprising 4-halophthalic anhydride provided by the presentinvention is reacted with a diamine such a m-phenylene diamine toprovide a bisimide comprising structure V. Polyetherimides may besynthesized by the reaction of the bis(halophthalimide) V

wherein X is halogen, with an alkali metal salt of a dihydroxysubstituted aromatic compound in the presence or absence of phasetransfer catalyst. Suitable phase transfer catalysts are disclosed inU.S. Pat. No. 5,229,482, which is herein incorporated by reference.Suitable dihydroxy substituted aromatic hydrocarbons include thosehaving the formula (VI)HO-A¹-OH  (VI)wherein A¹ is a divalent aromatic hydrocarbon radical. Suitable A¹radicals include m-phenylene, p-phenylene, 4,4′-biphenylene,4,4′-bi(3,5-dimethyl)phenylene, 2,3-bis(4-phenylene)propane and similarradicals such as those disclosed by name or formula in U.S. Pat. No.4,217,438. Bisphenol VI includes bisphenol A (BPA), bisphenol M,bisphenol Z and the like.

The A¹ radical preferably has the formula (VII)-A²-Q-A³-  (VII)wherein each of A² and A³ is a monocyclic divalent aromatic hydrocarbonradical and Q is a bridging hydrocarbon radical in which one or twoatoms separate A² from A³. The free valence bonds in formula (VII) areusually in the meta or para positions of A² and A³ in relation to Q. A²and A³ may be substituted phenylene or hydrocarbon-substitutedderivative thereof, illustrative substituents (one or more) being alkyland alkenyl, unsubstituted phenylene radicals are preferred. Both A² andA³ are preferably p-phenylene, although both may be o- or m-phenylene orone o- or m-phenylene and the other p-phenylene.

The bridging radical, Q, is one in which one or two atoms, preferablyone, separate A² from A³. Illustrative radicals of this type aremethylene, cyclohexylmethylene, 2-(2,2,1)-bicycloheptylmethylene,ethylene, isopropylidene, neopentylidene, cyclohexylidene, andadamantylidene. The preferred radical of formula (IV) is2,2-bis(4-phenylene)propane radical which is derived from bisphenol Aand in which Q is isopropylidene and A² and A³ are each p-phenylene.

It is clear to one of ordinary skill in the art that any impuritiespresent in the halophthalic anhydride will be carried through tosubsequent steps in the polyetherimide synthesis. The presence ofsignificant levels of impurities in subsequent steps can interfere withpolymerization and cause discoloration of the final product,polyetherimide.

As noted, in one aspect the present invention provides a method formaking a polyetherimide comprising structural units derived from ahalophthalic anhydride, itself made by the method of the presentinvention. Thus, the method for making a polyetherimide comprisescontacting in a liquid phase reaction mixture at least onehalogen-substituted ortho-xylene with oxygen and acetic acid at atemperature in a range between about 120° C. and about 220° C. in thepresence of a catalyst system. The catalyst system consists essentiallyof a source of cobalt ions, a source of manganese ions, and a source ofbromide ions. The reaction mixture is characterized by an initial molarratio of cobalt ion to halogen-substituted ortho-xylene of less thanabout 2%, an initial molar ratio of manganese ion to halogen-substitutedortho-xylene of less than about 1.5%, and an initial molar ratio ofbromide ion to halogen-substituted ortho-xylene of less than about 0.5%.The oxygen is present in an amount corresponding to a partial pressureof oxygen in a range between about 0.00001 and about 15 bar. There isobtained a product mixture comprising less than 10 percenthalogen-substituted ortho-xylene starting material, a halophthalic acidproduct, and less than about 10,000 parts per million halobenzoic acidby-product and less than 1000 parts per million halophthalide by-productbased on a total amount of halophthalic acid present in the productmixture. The product halophthalic acid is then dehydrated to form ahalophthalic anhydride which is typically purified by distillation priorto its condensation reaction with a diamine such as 1,3-diaminobenzeneto form bis(halophthalimide) V wherein X is a halogen; and subsequentlyreacting bis(halophthalimide) (V) with an alkali metal salt of adihydroxy substituted aromatic compound having the formula (VI) whereinA¹ is a divalent aromatic radical to form a polyetherimide.

In one embodiment the present invention provides a polyetherimidecomprising structural units derived from 4-chlorophthalic anhydride,m-phenylene diamine and bisphenol A.

The first product mixture comprises water, acetic acid, and hydrochloricacid. This product mixture can be further processed to recover aceticacid, which can be used in the oxidation process. In other embodiments,the first product mixture may comprise water and acetic acid; or water,acetic acid, hydrochloric acid, and methyl acetate. The presence ofhydrogen chloride is believed to be due to dehalogenation of one or moreof the starting materials (e.g., chloro o-xylene), the intermediates(e.g. 4-chloro-2-methylbenzoic acid), the product (e.g. 4-chlorophthalicacid), and by-products (e.g., 4-chlorophthalide) used in or formedduring the oxidation reaction of chloro o-xylene to chlorophthalic acid.Those skilled in the art will understand that the use of startingmaterials other than chloro o-xylene, for example bromo o-xylene, willproduce hydrogen bromide via analogous dehydrohalogenation processes.Typically, the HCl concentration in the vapor phase of the oxidationreaction medium is under 2000 ppm. In one embodiment, upon completion ofthe oxidation reaction, the first product mixture can be stripped toafford a crude chlorophthalic acid product and recovered acetic acidsolvent, which comprises water, acetic acid, and hydrochloric acid.

The crude recovered acetic acid solvent can be further purified by atleast one distillation step to afford purified acetic acid. The cruderecovered acetic acid solvent may be present as a component in amulticomponent mixture, for example a 2-component, 3-component,4-component, or 5-component mixture. The crude recovered acetic acidsolvent is sometimes referred to herein as a “feed stream” since itrepresents the material being fed to a solvent purification and recoverysystem. Non-limiting examples of 2-component, 3-component, 4-component,and 5-component feed-streams include acetic acid-water (2-component),acetic acid-water-HCl (3-component); and acetic acid-water-HCl-methylacetate (4-component), and acetic acid-water-HCl-methyl acetate-methanol(5-component) mixtures, respectively. The feed-stream may compriseacetic acid in any amount from greater than or equal to about 50 weightpercent to 99 weight percent. In one embodiment, multi-componentfeed-stream comprises at least 50 weight percent of acetic acid, lessthan about 4 weight percent HCl, and less than about 20 weight percentof methyl acetate. In another embodiment; a multi-component feed streamcomprises at least 65 weight percent of acetic acid, less than about 3.8weight percent of HCl, and less than about 5 weight percent of methylacetate. In yet another embodiment, a multi-component feed streamcomprises at least 82 weight percent of acetic acid, less than about 0.3weight percent of HCl, and less than about 2.5 weight percent of methylacetate. In each of the aforesaid embodiments, the multi-component feedstream may further comprise additional components such as water,chlorophthalic acids, chlorobenzoic acids, and bromide salts.

In one embodiment of the present invention the distillation stepcomprises introducing a mixture comprising water, acetic acid, andhydrochloric acid into a vertical distillation column, said columnhaving a top outlet adapted for the removal of an “overheads”(distillate) stream, a bottom outlet adapted for removing a “bottoms”(reboiler) stream, and a “side-draw” outlet adapted for removing a“side” stream. In one embodiment of the present invention, the“overheads” stream is “water-rich”, the “bottoms” stream is “aceticacid-rich” and the “side” stream” is “HCl-rich”. A water-rich overheadstream is defined herein as a mixture comprising greater than or equalto about 80 weight percent water. In an embodiment, the water richcomponent comprises greater than or equal to about 80 weight percent ofwater, less than or equal to about 20 weight percent of acetic acid, and0-500 ppm of HCl. When the feed stream further comprises methyl acetateand methanol (in addition to acetic acid, water and HCl), separation ofthe stream in a distillation column having a top outlet adapted for theremoval of an “overheads” stream, a bottom outlet adapted for removing a“bottoms” stream, and a “side-draw” outlet adapted for removing a “side”stream, the overheads stream is water rich comprising, in oneembodiment, between about 70 and about 100 weight percent of water,between 0 to about 1 weight percent of methanol, and between 0 and about30 weight percent of methyl acetate, and in another embodiment betweenabout 85 and about 100 weight percent of water, between 0 to about 1weight percent of methanol, and between 0 and about 15 weight percent ofmethyl acetate.

An HCl-rich side-draw stream is herein defined as a mixture comprisingfrom about 0.1-5 weight percent HCl, relative to the total weight of theside-draw stream, water in an amount corresponding to between about 25and about 35 percent by weight of the total weight of the side-drawstream, and acetic acid in an amount corresponding to between about 65and about 75 percent by weight of the total weight of the side-drawstream. In certain instances, the composition of the HCl-rich stream maycorrespond to that of a HCl-acetic acid-water azeotrope, which typicallyhas around 3.5 weight percent of HCl.

The acetic acid-rich bottoms stream is herein defined as a mixturecomprising at least 90 weight percent of acetic acid. Typically, thebulk of the remainder of the bottoms stream is made up of water,although other components may at times be present. Purification ofsolvent mixtures comprising acetic acid, water, and HCl, and optionallyother components such as methanol and methyl acetate may be performed ona laboratory-scale using an Oldershaw-type distillation columncomprising a top outlet adapted for the removal of an overheads stream,a bottom outlet adapted for removing a bottoms stream, and a side-drawoutlet adapted for removing a side-draw stream. Such distillationcolumns are available commercially from Normschliff Geratebau. Thedistillation column can be operated at sub-ambient, ambient, orsuper-ambient pressures. Operating pressure can be varied over a rangefrom about 100-5200 millibars in an embodiment, from about 300-3100millibars in another embodiment, and from about 800-1100 millibars instill another embodiment. The feed-stream is introduced into the columnvia a feed-port on the column in a manner so as to facilitate recoveryof the product either as a bottom stream or a top stream (distillate).The section of the column above the feed-port is referred to as therectification or enriching section, and the section of the column belowthe feed-port is referred to as the stripping section. In an embodiment,the undesired HCl is removed as the HCl-rich component as a side-drawabove the feed-port, and in another embodiment, the water-richcomponent, comprising minor amounts of acetic acid, and methyl acetateand methanol (if present) is removed as a distillate at the top of thecolumn. Acetic acid is removed as an acetic acid-rich component as thebottom stream (below the feed-port). The HCl content in the side-drawstream is generally about 1-3.5 weight percent, typically about 1.5-2.5weight percent. The acetic acid content in the side-draw stream isgenerally about 65-80 weight percent. The acetic acid-rich componentgenerally has a purity of at least 90 weight percent in an embodiment,greater than 95 weight percent in another embodiment, and greater thanor equal to about 98 weight percent in yet another embodiment. Invarious embodiments, it is possible to recover at least 75 weightpercent, at least 85 weight percent, and at least 95 weight percent ofhigh purity acetic acid, relative to the weight of acetic acid presentin the crude recovered acetic acid solvent. It is frequently possible torecover acetic acid having purity between about 95 to 99.9 percent theusing the distillation techniques described herein. The HCl content inthe acetic acid-rich component is typically less than about 500 ppm inanother embodiment, and less than 250 ppm in another embodiment.

EXAMPLES

The following examples are set forth to provide those of ordinary skillin the art with a detailed description of how the methods claimed hereinare carried out and evaluated, and are not intended to limit the scopeof what the inventors regard as their invention. Unless indicatedotherwise, parts are by weight, temperature is in ° C. In Tables 1 and2, values given for analytical measurements are bracketed ( ) whenmeasured by HPLC. Otherwise values were determined using gaschromatography.

Oxidation Halo Ortho Xylenes to Halophthatlic Acids

Laboratory scale reactions were carried out in a 3.5 liter, pressurizedHastelloy C22 reaction vessel adapted for heating and cooling, andequipped with a mechanical agitator, a gas inlet valve attached to asubsurface gas inlet tube, an internal thermocouple, a pressuretransducer, and a gas outlet valve linked to a condenser and receivingvessel operated at atmospheric pressure. The chloro-o-xylene startingmaterial was typically a mixture of 3-chloro and 4-chloro isomers. The3-, 4-isomer ratio was determined by ¹H-NMR and gas chromatography (GC).Acetic acid was employed as the reaction solvent. The catalyst systemtypically consisted of cobaltous acetate, manganous acetate and sodiumbromide and was charged to the reaction vessel under ambient conditionsas a 15-16% solution in acetic acid. In some instances sodium acetatewas added as an anticorrosive agent. After the reactants had beencharged, the reaction vessel was sealed and the vessel was placed in atest cell, pressurized with nitrogen to about 19 bar and heated to theinitial reaction temperature, typically about 160° C. while stirring thereaction mixture at about 800 rpm. Compressed air was then introduced asthe source of oxygen at a rate such that the concentration of oxygen inthe effluent gas emerging from the gas outlet valve was less than about2%, typically about 0.5-1.0%. Initially, the flow of air was relativelymodest, but then was increased such that the oxygen level in theeffluent gas was maintained in the range of about 0.1 to about 1.0%. Anexotherm was observed as the reaction initiated and appropriate coolingwas employed to maintain a temperature of 160° C. After about 60minutes, the set-point temperature was increased to 175° C. The rate ofaddition of the additional compressed air was regulated such that theconcentration of oxygen in the gas emerging from the reactor at the gasoutlet valve comprised less than about 1%. When most of thechloro-o-xylene had been consumed, it was observed that the amount ofoxygen present in the gas emerging from the reactor at the gas outletvalve rose rapidly. This rapid rise in oxygen concentration in the gasstream emerging from the gas outlet valve was referred to as “oxygenbreakthrough” and indicated that the reaction had entered a“post-oxidation” phase in which the bulk of the starting chloro-o-xylenehad been consumed. In this post-oxidation phase of the reaction, a phasecharacterized by the high conversion (>90%) of starting material toproducts and decreasing reaction rate, the compressed air employed asthe stoichiometric oxidant was further diluted with nitrogen such thatthe gas stream exiting the reactor at the gas outlet valve containedless than about 4% oxygen. Typically, the temperature of the reactionmixture was raised to about 190° C. at the outset of the post-oxidationphase and was maintained at that temperature for a period of from about0.5 to about 3 hours. The total amount of oxygen fed to the reactor wastypically 110-130% of that required for stoichiometric reaction (3 molof O₂/mol of chloroxylene). Upon completion of the reaction, thehomogeneous reaction mixture was assayed by high performance liquidchromatography (HPLC) and gas chromatography (GC). Typically, conversionof starting chloro-o-xylene to product chlorophthalic acid wassubstantially in excess of 90% and the concentration of chlorobenzoicacid by-product was less than about 10,000 ppm and the concentration ofhalophthalide by-product was less than about 1000 ppm based on the totalamount of halophthalic acid present in the product mixture.

Example 1

A 3.5 liter reaction vessel equipped as described above was charged witha 95:5 mixture of 4-chloro-o-xylene and 3-chloro-o-xylene (492.1g, 3.50mol), acetic acid (1925 mL, 32.06 mol), cobaltous acetate tetrahydrate(13.1 g, 0.0526 mol, 1.50 mole % based on 3.5 moles of 3- and4-chloro-o-xylene), manganous acetate tetrahydrate (6.4g, 0.0261 mol,0.75 mole % based on 3.5 moles of 3- and 4-chloro-o-xylene), sodiumbromide (0.6g, 0.0060 mol, 0.17 mole % based on 3.5 moles of 3- and4-chloro-o-xylene), and sodium acetate (2.9 g, 0.0354 mol, 1.01 mole %based on 3.5 moles of 3- and 4-chloro-o-xylene). The reaction vessel wassealed and pressurized with nitrogen to 19 bar and then heated to about160° C. Compressed air was then introduced into the reaction mixture ata rate such that the concentration of oxygen in the gas emerging fromthe reactor gas outlet valve was about 0.5%. The reaction temperaturewas maintained at about 160° C. for 1 hour and was then raised to about175° C. and was maintained at that temperature until “oxygenbreakthrough” was noted. Oxygen breakthrough marked the beginning of thepost-oxidation phase of the reaction. The compressed air being fed tothe reactor was then diluted with sufficient nitrogen to limit theconcentration of oxygen in the gas emerging from the reactor gas outletvalve to less than about 2%. The reaction temperature was raised toabout 190° C. and maintained at that temperature throughout thepost-oxidation phase which lasted approximately three hours. Thereaction mixture was then assayed by BPLC and GC and found to containthe product diacids as a mixture of 3-chlorophthalic acid and4-chlrorophthalic acid containing less than 10,000 ppm chlorobenzoicacids. Conversion of starting material to products was in excess of 90percent.

Examples 2-14

Data for a series of oxidation reactions conducted as described inExample 1 together with modifications to reaction parameters indicatedare gathered in Table 1. The data demonstrate the effectiveness of themethod of the present invention to produce high yields of chlorophthalicacid while limiting the amount of chlorobenzoic acid by-products. InTable 1 the header “Variation” refers to the reaction parameter beingvaried in the Example, “standard” refers to the amounts of reagents andreaction conditions used in Example 2 which are given below.

Conditions of Example 2:

(A) Reagents

492.1 g (3.5 Mol) 3-/4-Chloro-1,2-dimethylbenzene (95% 4-isomer + 5%3-isomer) 1925 g acetic acid 13.1 g (52.5 mMol) Cobaltous acetatetetrahydrate 6.4 g (26.25 mMol) Manganous acetate, tetrahydrate 0.65 g(6.3 mMol) sodium bromide 12.3 g (150.0 mMol) sodium acetate (anhydrous)(B) Oxidation Conditions

19 bar_(abs) nitrogen pressure, stirrer speed 800 rpm. Temperature 152°C. at initial oxygen introduction. Cooling begun immediately uponreaction initiation to maintain an internal temperature of about 160° C.After 60 min the temperature was raised to 175° C. At the beginning ofthe post-oxidation phase of the reaction the temperature was raised to190° C. for a period of 60 minutes.

Induction period: <1 min Reaction time: 144 min + 60 min post reactionat 190° C. Reaction Temp.: first 160–161° C., then 173–177° C., end 190°C. Pressure: 19 bar_(abs) Gas flow rates: initial 1050 l/h (scaled value210 l/h), much slower at “EOR”.

Still referring to Table 1, the term “air input” refers to the variationin which the reaction was “oxygen limited” meaning that the gas flowrate was initially 900 l/h (scaled value 180 l/h), much slower at theend of the reaction (“EOR”). The heading “Oxidation Conds.” refers tothe conditions employed in the oxidation reaction which were either (1)the “standard” conditions as given for Example 2 or the “oxygen limited”reaction conditions of Examples 4 and 5. The heading “Post-OxidationConds.” refers to the duration (time) and temperature of the reactionfollowing “oxygen breakthrough”. The heading “Cl-phthalic acid” refersto the total amount of 3- and 4-chlorophthalic acid present in the crudeproduct mixture at the end of the oxidation reaction. The values givenin the column headed “Cl-phthalic acid” are the combined “area percent”of the peaks attributed to 3- and 4-chlorophthalic acid in a gaschromatogram of the crude product mixture. The heading “Isomeric CIBA's”refers to the total amount of 2-, 3-, and 4-chlorobenzoic acids presentin the crude reaction mixture and expressed in parts per million (ppm).2-chlorobenzoic acid, 3-chlorobenzoic acid, and 4-chlorobenzoic acid arebelieved to arise by decarboxylation of 3-chlorophthalic acid and4-chlorophthalic acid.

TABLE 1 OXIDATION OF CHLOROXYLENE TO CHLOROPHTHALIC ACID Oxidation-Post- Cl-phthalic Isomeric Example Trial-No. Variation Conds. Oxidationacid^(a) ClBA's 2 128a Standard Standard 60 min/190° C. 97.6% (1334) 3130a Standard Standard 60 min/190° C. 97.0–98.5 (0961) 4 131a air-inputO2- 60 min/190° C. 97.6 (1371) limited 5 135a 0.22 Mol % O2- None97.0–98.5 (0837) Br limited 6 136a 0.22 Mol % Standard 60 min/190° C.97.0–98.5 (0843) Br 7 137a 150% Standard 60 min/190° C. 97.0–98.5 (0941)Catalyst 8 138a Postoxidation Standard 30 min/190° C. 97.0–98.5 (0897)time 30 min 9 148a 50% Standard 60 min/190° C. 97.0–98.5 (0926) Catalyst10 149a 0.14 Mol % Standard 60 min/190° C. 97.0–98.5 (1261) Br 11 150alow Standard 60 min/190° C. 97.0–98.5 (1244) NaOAc- level 12 152a 10%less Standard 60 min/190° C. 97.0–98.5 (1185) Mn 13 153a StandardStandard 60 min/190° C. 97.0–98.5 (1536) 14 154a low Standard 60min/190° C. 97.0–98.5 (1435) NaQAc- level ^(a)% of peak total peak area(HPLC) attributed to halophthalic acids, halobenzoic acids andhalophthalides. All values fell in a range between 97.0 and 98.5%.Conversion of Halophthalic Acids to Halophthalic Anhydrides

Example 2a Cyclization Procedure Using Acetic Anhydride

The crude reaction product of Example 2 was divided into two identicalfractions each weighing 1355 grams. One of the two fractions wassubjected to distillation at atmospheric pressure (pot temperature 150°C.) until a total of about 952.9 grams of a mixture of water and aceticacid had been collected in the receiving vessel. The maximum headtemperature was 122° C. When the head temperature reached 122° C. aceticanhydride (196.5 g, 1.93 mole) was added dropwise to the distillationflask and the resultant blue solution (no precipitate was observed) washeated at reflux (136° C.) for a two hour period. A mixture of aceticacid and acetic anhydride (198.6 grams) was then distilled off atatmospheric pressure (pot temperature 160° C.). Thereafter, vacuum wascarefully applied to remove any remaining acetic anhydride, and theproduct chlorophthalic anhydride was distilled under vacuum. Twofractions were collected, the first distilled at 70-98° C. at a pressurein a range between 18 and 645 mbar. The first fraction (81.2 grams)contained residual acetic acid, acetic anhydride and productchlorophthalic anhydride. The second fraction distilled at between 136and 144° C. at a pressure in a range between 3 and 5 mbar. The secondfraction consisted essentially of a mixture of 3- and 4-chlorophthalicanhydride (276.6 g, 1.52 mole, 86.6% of theory). Examples 3a-14a werecarried out as described for Example 2. Data are gathered in Table 2.

Example 14b Thermal Cyclization Procedure

The crude reaction product of Example 14 was sampled for analysis andthen divided into two identical fractions (fractions “a” and “b”) eachweighing 1351 grams. Fraction “b” was charged to a 2-liter flask.Distillation was carried out at atmospheric pressure (maximum pottemperature 175° C.) until a total of about 1012.8 grams of distillatehad been removed. Vacuum was then carefully applied until a pressure ofabout 80 mbar was achieved and the mixture was heated under vacuum forabout 3 hours at 175° C. to effect ring closure and water removal. Thecrude anhydride was vacuum distilled to afford purified chlorophthalicanhydride (282.6 g, 88.5%) as a colorless solid.

TABLE 2 CONVERSION OF HALOPHTHALIC ACID TO HALOPHTHALIC ANHYDRIDE Trial-% Yield Example No. ClPA [5-ClP]^(a) [4-ClP]^(b) [PA]^(c) [ClBA]^(d)  2a128a 86.6 <100 (18) <100 2300  100/400  3a 130a 84.8 <100 <100 2400 1200 3b 130b 63   <100 <100 2500 3900  4 131a 89.6 <100 (29) <100 2500  900(91)  5 135a 86.4 1100 100 2500 7600  6 136a 87.4 <100 (19) <100 23002900 (184)  7 137a 83.2 <100 (15) <100 2200 8800 (126)  8 138a 88.5  200 (119) <100 2200 2800 (167)  9 148a 85.8 <100 (20) <100 2200 2500(219) 10a 149a 81.4 <100 (19) <100 2500 3400 (210) 11a 150a 88.3 <100(16) <100 2600 4200 (111) 11b 150b 87.2 <100 (16) <100 2500 3400 12a152a 89.5 <100 (20) <100 2200 3600 (203) 12b 152b — <100 (23) <100 24003100 13a 153a 88.4 <100 (21) <100 2300 2200 (194) 14a 154a 88.9 <100(18) <100 2900 6100 (214) 14b 154b 88.5 — — — — ^(a)5-chlorophthalide(ppm) ^(b)4-chlorophthalide (ppm) ^(c)phthalic acid (ppm) ^(d)totalisomeric chlorobenzoic acids (ppm)

The data provided in Tables 1 and 2 clearly demonstrate the surprisingefficacy of the method of the instant invention. FIGS. 1-3 were preparedusing data from experiments carried out during the studies comprisingthe instant invention. FIG. 1 shows the effect of the post-oxidationconditions on the yields of product and by-products formed in theoxidation reaction. The data show that lower levels of chlorophthalidesare obtained at post-oxidation times of 30 minutes or longer at 190° C.FIG. 2 illustrates the surprising influence of bromide level on thereaction outcome. Unexpectedly, for the oxidation of chloro-ortho-xyleneunder “standard” conditions, a bromide level in a range between about0.14 and about 0.22 mole percent (relative to the initial amount ofchloro-ortho-xylene) provides much lower levels of impurities. FIG. 3illustrates the surprising influence of the catalyst concentration onthe level of impurities found in the reaction product. FIG. 3 shows thathigher levels of undesired chlorobenzoic acid impurities are formed whenthe catalyst level (combined “Co” and “Mn”) exceeds about 3 molepercent.

Example 15 General Procedure for the Recovery of Acetic Acid

Acetic acid purification was carried out using a laboratory Oldershawtype distillation column having a total of 62 stages, which included a60 plate perforated plate column, a reboiler and a condenser. The columnhad a silver vacuum jacket, an inner diameter of 30 mm, 80 holes perplate, an operating hold-up of 2 ml/plate, a hold-up volume of 0.15ml/plate, and a column plate efficiency of 66%. The reboiler had acapacity of 6 liters with a 1000 Watt heater, controllable to desiredpower input. Reflux ratio was controlled on a time basis with anelectromagnetically-controlled column head in conjunction withelectronic controllers. Water was used as coolant for the condenser. Thedistillation set-up also included probes for measuring temperature atthe column top and reboiler, probes for measuring the pressure in thereboiler and the pressure drop across the column; as well as provisionsfor pre-heating the feed-stream and sampling the streams emanating fromthe column. The distillation column was configured to have 5 ports,ports 1, 2, 3, 4, and 5, corresponding to stages 9, 17, 25, 39, 47, and55, respectively. Stage 1 refers to the top tray, and stage 62 refers tothe bottom tray. Peristaltic pumps were used to pump the feed and bottomstreams. A pump was used to withdraw the side-draw stream. Mass flowrates were measured gravimetrically using electronic weighing balances.The column was operated under ambient pressure using the range ofoperating parameters shown in Table 3.

TABLE 3 Operating Parameter Value Feed-stream pump rate (gm/hour) 80–110 Side-draw withdrawal rate (gm/hour)   5–7.5 Bottom streamwithdrawal rate (gm/hour) 65–90 Heat (i/p) in Watts 160–180 Reflux ratio  6–7.5 Overhead stream take-off rate (gm/hour)   5–17.5 Pressure drop(millibar) 65–75 Pressure at reboiler (millibar) 950–980 Overheadtemperature (° C.)  80–100 Bottom temperature (° C.) 116–120

Comparative Example 1

In this Example, no side-draw was used in the distillation. A refluxratio of 6 was used. The compositions of the fractions sampled at thevarious stages are shown in Table 4. The weight percent of water, whichmade up the remainder of each samples is not shown.

TABLE 4 Composition (Weight percent) Stage Number Acetic acid HClDistillate 58.9 0.43  9 69.8 3.71 17 68.9 3.78 25 69.4 3.77 39 70.3 3.67Feed (47) 84.1 0.24 55 85.7 1.43 Reboiler (62) 89.0 0.20

Example 16

A reflux ration of 6 and a side draw from stage 25 of the distillationcolumn was employed. The compositions of the fractions sampled at thevarious stages are shown in Table 5. The weight percent of water, whichmade up the remainder of each samples is not shown.

TABLE 5 Composition (Weight percent) Stage Number Acetic acid HClDistillate 15.7 <0.01  9 23.9 0.00 17 45.6 0.02 Side draw (25) 70.7 2.2639 70.3 2.82 Feed (47) 85.2 0.15 55 91.1 0.07 Reboiler (62) 99.2 <0.01

Example 17

A reflux ratio of 6 and a side draw from stage 39 of the distillationcolumn was used. The compositions of the fractions sampled at thevarious stages are shown in Table 6. The weight percent of water, whichmade up the remainder of each samples is not shown.

TABLE 6 Composition (Weight percent) Stage Number Acetic acid HClDistillate 9.6 <0.01  9 16.5 <0.01 17 32.3 <0.01 25 62.0 0.40 Side draw(39) 71.3 2.60 Feed (47) 83.5 0.20 55 98.4 0.05 Reboiler (62) 99.3 <0.01

Example 18

A reflux ratio of 6 was used. The compositions of the fractions sampledat the various stages are shown in Table 7. The weight percent of water,which made up the remainder of each samples is not shown.

TABLE 7 Composition (Weight Percent) Stage Number Acetic acid HCl Methylacetate Methanol Distillate 12.0 <0.01 17.01 0.29  9 27.6 <0.01 <0.3<0.06 17 56.7 0.23 <0.3 <0.06 25 69.2 3.02 <0.3 <0.06 Side draw (39)73.0 2.37 <0.3 <0.06 Feed (47) 84.9 0.16 1.98 <0.06 55 >99.5 <0.01 <0.3<0.06 Reboiler (62) . 99.8 , 0.01 , 0.3 , 0.06

Example 19

A reflux ratio of 7.5 was used. The compositions of the fractionssampled at the various stages are shown in Table 8. The weight percentof water, which made up the remainder of each samples is not shown. “ND”stands for “not detected”.

TABLE 8 Composition (Weight Percent) Stage Number Acetic HCl MethylMethanol Distillate 7.0 <0.01 16.10 0.42 9 14.1 <0.01 ND ND 17 28.7<0.01 ND ND 25 34.2 0.04 ND ND Side draw (39) 70.3 2.91 ND ND Feed (47)85.0 0.16 1.85 <0.06 55 >99.5 <0.01 ND ND Reboiler (62) >99.8 <0.01 NDNDExamples 16-19 illustrate the utility of withdrawing the side-drawstream in order to recover high purity acetic acid containing less than0.01 weight percent of hydrochloric acid from aqueous feed streamscomprising acetic acid and aqueous HCI; and acetic acid, aqueous HCI,methyl acetate, and methanol.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood by thoseskilled in the art that variations and modifications can be effectedwithin the spirit and scope of the invention.

1. A method of preparing a halophthalic acid, said method comprising thesteps of: contacting in a liquid phase reaction mixture at least onehalogen-substituted ortho-xylene with oxygen and acetic acid at atemperature in a range between about 120° C. and about 220° C. in thepresence of a catalyst system, said catalyst system consistingessentially of a source of cobalt ions, a source of manganese ions, anda source of bromide ions, said reaction mixture being characterized byan initial molar ratio of cobalt ion to halogen-substituted ortho-xyleneof less than about 2%, an initial molar ratio of manganese ion tohalogen-substituted ortho-xylene of less than about 1.5%, and an initialmolar ratio of bromide ion to halogen-substituted ortho-xylene of lessthan about 0.5%, said oxygen being present in an amount corresponding toa partial pressure of oxygen in a range between about 0.00001 and about15 bar, to provide a product mixture comprising less than 10 percenthalogen-substituted ortho-xylene starting material, a halophthalic acidproduct, and less than about 10,000 parts per million halobenzoic acidby-product and less than 1000 parts per million halophthalide by-productbased on a total amount of halophthalic acid present in the productmixture.
 2. The method according to claim 1 wherein the product mixturecomprises less than about 5,000 parts per million halobenzoic acid. 3.The method according to claim 2 wherein the product mixture comprisesless than about 1,000 parts per million halobenzoic acid.
 4. The methodaccording to claim 1 wherein said contacting is carried out at atemperature in a range between about 150° C. and about 200° C.
 5. Themethod according to claim 1 wherein said at least onehalogen-substituted ortho-xylene is a mixture of3-chloro-1,2-dimethylbenzene and 4-chloro-1,2-dimethylbenzene.
 6. Themethod according to claim 5 wherein said mixture comprises about 95 molepercent 3-chloro-1,2-dimethylbenzene.
 7. The method according to claim 5wherein said mixture comprises about 95 mole percent4-chloro-1,2-dimethylbenzene.
 8. The method according to claim 1 whereinsaid at least one halogen-substituted ortho-xylene consists essentiallyof 4-chloro-1,2-dimethylbenzene.
 9. The method according to claim 1wherein said source of cobalt ions is at least one cobalt containingspecies selected from the group consisting of metallic cobalt, salts ofcobalt, and organometallic compounds containing cobalt.
 10. The methodaccording to claim 1 wherein said source of cobalt ions is comprises atleast one of cobalt sulfate, cobalt bromide, cobalt chloride, cobaltfluoride, cobalt iodide, cobalt nitrate, cobalt stearate, cobaltcarbonate, cobalt naphthalate, Co(OH)2, cobalt phosphate, cobalt (DI)fluoride, cobaltous acetate, cobalt (II) acetylacetonate, cobalt (IT)benzoylacetonate, cobalt(m) acetylacetonate, and cobalt (IT)hexafluoroacetylacetonate.
 11. The method according to claim 1 whereinsaid source of manganese ions is at least one manganese containingspecies selected from the group consisting of metallic manganese, saltsof manganese, and organometallic compounds containing manganese.
 12. Themethod according to claim 1 wherein said source of manganese ionscomprises at least one of manganese (II) fluoride, manganese (II)chloride, manganese (II) bromide, manganese (II) iodide, manganese (III)fluoride, manganese (II) acetate, manganese sulfate, manganese nitrate,manganese carbonate, manganese (II) acetate, manganese (II)acetylacetonate, manganese (III) acetylacetonate, manganese (II)hexafluoroacetylacetonate, and manganese (III)hexafluoro-acetylacetonate.
 13. The method according to claim 1 whereinsaid source of bromide ions is at least one bromine-containing speciesselected from the group consisting of inorganic bromide salts, organicbromide salts, inorganic bromine compounds comprising covalently boundbromine, organic bromine compounds comprising covalently bound bromine,BrCl, and elemental bromine.
 14. The method according to claim 1 whereinsaid source of bromide ions comprises at least one of alkali metalbromide, alkaline earth metal bromides, lanthanide metal bromide,transition metal bromides, quaternary ammonium bromides, quaternaryphosphonium bromides, tetrabromosilane, acetyl bromide, oxalyl bromide,carbonyl dibromide, and tertiary-butyl bromide.
 15. The method accordingto claim 1 wherein said source of cobalt is less than about 1.5 molepercent based on the halogen-substituted ortho-xylene.
 16. The methodaccording to claim 1 wherein said source of manganese is less than about1.0 mole percent based on the halogen-substituted ortho-xylene.
 17. Themethod according to claim 1 wherein said source of bromide is less thanabout 0.35 mole percent based on the halogen-substituted ortho-xylene.18. The method according to claim 1 wherein the product mixturecomprises less than about 5 percent of halogen-substituted ortho-xyleneand less than 10,000 parts per million halobenzoic acid.
 19. The methodaccording to claim 1, wherein the method further comprises addition ofat least one diluent gas.
 20. The method according to claim 19, whereinsaid diluent gas comprises nitrogen.
 21. The method according to claim1, wherein the partial pressure of oxygen in a range between about 0.001and about 10 bar.
 22. The method according to claim 1, wherein theacetic acid is present in an amount of between about 3 and 7 parts byweight per 1 part of halosubstituted ortho-xylene.
 23. A method ofpreparing a chlorophthalic acid, said method comprising the steps of:contacting in a liquid phase reaction mixture at least onechloro-substituted ortho-xylene with oxygen and acetic acid at atemperature in a range between about 120° C. and about 220° C. in thepresence of a catalyst system, said catalyst system consistingessentially of a source of cobalt, ion, a source of manganese ions, anda source of bromide ions, said reaction mixture being characterized byan initial molar ratio of cobalt (II) acetate to chloro-substitutedortho-xylene of less than about 2%, an initial molar ratio of manganese(II) acetate to chloro-substituted ortho-xylene of less than about 1.5%,and an initial molar ratio of sodium bromide to chloro-substitutedortho-xylene of less than about 0.5%, said oxygen being present in anamount corresponding to a partial pressure of oxygen in a range betweenabout 0.00001 and about 15 bar, to provide a product mixture comprisingless than 10 percent chloro-substituted ortho-xylene starting material,a chlorophthalic acid product, and less than about 10,000 parts permillion chlorobenzoic acid by-product and less than about 1000 parts permillion chlorophthalide based on a total amount of chlorophthalic acidpresent in the product mixture.
 24. A method of preparing a halophthalicacid, said method comprising the steps of: Step (A) contacting in aliquid phase reaction mixture at least one halogen-substitutedortho-xylene with oxygen and acetic acid at a temperature in a rangebetween about 120° C. and about 220° C. in the presence of a catalystsystem, said catalyst system consisting essentially of a source ofcobalt ion, a source of manganese ions, and a source of bromide ions,said reaction mixture being characterized by an initial molar ratio ofcobalt ion to halogen-substituted ortho-xylene of less than about 2%, aninitial molar ratio of manganese ion to halogen-substituted ortho-xyleneof less than about 1.5%, and an initial molar ratio of bromide ion tohalogen-substituted ortho-xylene of less than about 0.5%, said oxygenbeing present in an amount corresponding to a partial pressure of oxygenin a range between about 0.0001 and about 15 bar, to provide a firstproduct mixture comprising less than 10 percent halogen-substitutedortho-xylene starting material, a halophthalic acid product, and lessthan about 10,000 parts per million halobenzoic acid by-product and lesthan 1000 parts per million halophthalide based on a total amount ofhalophthalic acid present in the first product mixture; and Step (B)stripping a mixture comprising water, acetic acid, and hydrochloric acidfrom the first product mixture; to afford a crude recovered acetic acidsolvent comprising water, acetic acid, and hydrochloric acid.
 25. Themethod according to claim 24 wherein the crude recovered acetic acidsolvent is purified by at least one distillation step.
 26. The methodaccording to claim 25 wherein said distillation step comprisesintroducing a mixture comprising water, acetic acid, and hydrochloricacid into a distillation column and removing from said column awater-rich component, an acetic acid-rich component and an HCl-richcomponent.
 27. The method according to claim 26 wherein said water-richcomponent is removed as a overheads stream comprising between about 85and about 100 percent by weight water, from 0 to about 1 percent byweight methanol, and from 0 to about 15 percent by weight methylacetate.
 28. The method according to claim 26 wherein said aceticacid-rich component is removed as a bottoms stream comprising betweenabout 95 and about 99.9 percent by weight acetic acid.
 29. The methodaccording to claim 26 wherein said HCl-rich component is removed as aside-draw stream.
 30. The method according to claim 29 wherein saidHCl-rich component comprises hydrochloric acid in a an amountcorresponding to between about 0.1 and about 5.0 percent by weight ofthe total weight of the side-draw stream, water in a an amountcorresponding to between about 25 and about 35 percent by weight of thetotal weight of the side-draw stream, and acetic acid in a an amountcorresponding to between about 65 and about 75 percent by weight of thetotal weight of the side-draw stream.